Vical Incorporated of San Diego, CA is developing a bivalent CMV DNA vaccine for use in prevention of CMV disease and its consequences in transplantation. The vaccine, VCL-CBO 1, contains two plasmids, one encoding the major surface protein gB, and the other encoding the tegument protein pp65, and is formulated in the poloxamer CRL1005 to increase the induction of T cell and B cell responses. Immune responses to natural CMV infection have been used a model for the measurement of CIM" and CD8 T cells, but whether these assays will be applicable as surrogate markers of immunity in CMV vaccine trials has not been fully investigated. The objective of this Hyperaccelerated Award application will be to use the blood samples collected during the Vical Phase 1 and Phase 2 Trials to develop appropriate GLP assays that can be used to monitor vaccine responses in both CMV seropositive and CMV seronegative subjects, and to develop correlates of immunologic response with clinical and virologic outcomes. The specific AIMS will be to: 1) Determine the level of induction of T cell responses induced by VCL-CB01 using a peptide-based ELISPOT technique and intracellular cytokine cytometry (ICC) method, comparing the two methods to each other and to conventional lymphoproliferative assays. We will differentiate between the natural fluctuations in the CMV T-cell response and vaccine induced responses in CMV seropositives by longitudinal measurement of responses to the vaccine-encoded antigen, pp65, and another CMV antigen not included in the vaccine (IE1). 2) Compare and contrast DNA-vaccine induced T cell responses with those resulting from natural infection in seronegative and seropositive subjects through the use of multiparameter flow cytometry, MHC Class I tetramer binding studies and mapping of pp65 epitopes to the level of the 15-mers used in these assays. 3) Examine and develop novel methods for the measurement of neutralizing antibodies to CMV. These studies will be significant to the field in many ways. First, we will establish a relationship between vaccination and responses to natural infection that have been studied in a limited number of systems. We will discover whether the immunodominant responses to vaccination are similar to those induced by natural infection. We will study the immune responses to vaccination in the setting of potent natural immunity, which may be important in the area of therapeutic vaccines. We will determine in part the memory and effector phenotype of the T cells induced by DNA vaccination, and be able to compare these phenotypes to those induced by natural infection by other pathogens or by other vaccination modalities in the future. Lastly, we will further the field of measurement of CMV neutralization, which will be critical in the area of maternal-fetal disease prevention and possible universal vaccination.